The present invention relates to a brake pedal apparatus for inputting an operational force of a driver into a brake system for actuating brakes and, more particularly, to a brake pedal apparatus of which the lever ratio (hereinafter, referred to as xe2x80x9cpedal leveragexe2x80x9d) is changeable.
In most brake systems for automobiles, brakes are actuated by pedaling force applied by depressing a brake pedal.
FIG. 17 is an illustration schematically showing the basic structure of a typical conventional brake system with a brake pedal. In FIG. 17, numeral 1 designates a brake system, 2 designates a brake pedal for brake operation, 3 designates a booster for amplifying the pedaling force on the brake pedal 2 by power such as fluid pressure, negative pressure, or air pressure (positive pressure), 4 designates a tandem-type master cylinder (hereinafter, sometimes referred to as xe2x80x9cMCYxe2x80x9d) which is actuated by the output of the booster 3 to develop master cylinder pressure, 5 and 6 designate wheel cylinders (hereinafter, sometimes referred to as xe2x80x9cWCYsxe2x80x9d) of a first brake circuit which generate braking force by the MCY pressure supplied as braking pressure to them, 7 and 8 designate WCYs of a second brake circuit which generate braking force by the MCY pressure supplied as braking pressure to them, and 9 designates a reservoir of the MCY 4.
In this brake system 1, an input shaft 3a of the booster 3 is advanced (moved to the left in FIG. 17) by depression of the brake pedal 2 and the booster 3 thus amplifies the pedaling force to output amplified power. By the output of the booster 3, the MCY 4 is actuated to develop MCY pressure which is then supplied to the respective wheel cylinders 5, 6, 7, 8, thereby actuating brakes with large braking force i.e. amplified pedaling force.
By the way, in such a brake system 1, the lever ratio (L1+L2)/L1 of a lever 2a of the brake pedal 2, i.e. the pedal leverage, is normally constant, wherein L1 is a distance between a pivot of the lever 2a and a connection point where the input shaft 3a of the booster 3 is connected to the lever 2a, and L2 is a distance between the connection point and the center of the brake pedal 2. The constant pedal leverage leads to the following problems:
(1) in case of failure of amplifying action of the booster 3 (for example, power source failure), required pedaling force should be too large;
(2) under some condition, the pedal stroke may be increased, thus giving the driver a bad pedaling feel;
(3) a driver such as an inexpert driver may not produce large braking force even in case of emergency braking;
(4) the brake pedal may largely shift to the driver during a vehicle collision; and
(5) in such a design for improving the fuel consumption rate that brake pads are spaced largely (there is a limitation of spacing because the loss stroke of the brake pedal 2 should be considered) apart from brake disks or brake drums to prevent brake calipers from dragging, the pedal stroke should be longer.
Though there is a conventional pedal apparatus in which the pedal leverage can be adjusted by changing the joint position between the lever 2a of the brake pedal 2 and the input shaft 3a of the booster 3 (or the input shaft of the MCY 4) in case of booster failure, this apparatus can not completely solve the aforementioned problems and, in addition, the operation for changing the joint position is troublesome.
It is an object of the present invention to provide a brake pedal apparatus capable of easily changing its pedal leverage and therefore solving the aforementioned problems.
To achieve the aforementioned object, a brake pedal apparatus of the present invention comprises: a first lever member of which a middle portion is pivotally supported to a vehicle body by a first pivot pin; a second lever member which is provided at its one end with a pedal member and is pivotally connected to one end of said first lever member by a second pivot pin and to which an input shaft of a booster or an input shaft of a master cylinder is pivotally connected; a pivotal movement control means for controlling said first lever member in such a manner as to prevent the pivotal movement of said first lever member when a predetermined condition is not satisfied and to allow the pivotal movement of said first lever member when the predetermined condition is satisfied; and a coupling means for coupling said first and second lever members to pivot together when the pivotal movement of said first lever member is allowed.
The present invention is also characterized in that an end of said second lever member positioned opposite to said pedal member is pivotally connected to the end of said first lever member positioned opposite to said pedal member, and the input shaft of said booster or the input shaft of said master cylinder is pivotally connected to the second lever member at a position on the pedal member side relative to said first pivot pin.
Further, the present invention is characterized in that a middle portion of said second lever member is pivotally connected to the end of said first lever member positioned at the pedal member side, and the input shaft of said booster or the input shaft of said master cylinder is pivotally connected to the second lever member at a position on the side opposite to said pedal member relative to said first pivot pin.
In addition, the present invention is characterized in that said second lever member and the input shaft of said booster or said master cylinder are pivotally connected via a third lever member.
The present invention is also characterized in that said pivotal movement control means comprises: a receiving portion disposed at a position of said vehicle body which corresponds to the one end of said first lever member; an engaging means disposed on the one end of said first lever member and capable of engaging said receiving portion; and an engagement control means for controlling the engagement between said engaging means and said receiving portion in such a manner as to disengage said engaging means by the satisfaction of said predetermined condition, which engages said receiving portion to prevent the pivotal movement of said first lever member, from said receiving portion to allow the pivotal movement of said first lever member.
The present invention is characterized in that said predetermined condition is whether the pedaling force exceeds a preset threshold value or not, and said engagement control means controls the engagement in such a manner as to maintain said engaging means in the engaged state with said receiving portion when said pedaling force is smaller than the preset threshold value and to disengage said engaging means from said receiving portion when said pedaling force exceeds said preset threshold value.
Furthermore, the present invention is characterized in that said predetermined condition is whether the pedaling force exceeds a first preset threshold value or not and whether the pedal stroke exceeds a second preset threshold value or not, and said engagement control means controls the engagement in such a manner as to disengage said engaging means from said receiving portion only when said pedaling force exceeds said first threshold value and said pedal stroke is smaller than said second threshold value.
The present invention is characterized in that said predetermined condition is whether the pedaling speed exceeds a preset threshold value or not, and said engagement control means controls the engagement in such a manner as to maintain said engaging means in the engaged state with said receiving portion when said pedaling speed exceeds the preset threshold value and to disengage said engaging means from said receiving portion when said pedaling speed is lower than said preset threshold value.
The present invention is characterized in that said predetermined condition is whether said pedal member is moved backward from its inoperative position or not, and said engagement control means controls the engagement in such a manner as to disengage said engaging means from said receiving portion when said pedal member is moved backward from its inoperative position.
The present invention is characterized in that said predetermined condition is whether the pedal stroke exceeds a preset threshold value or not, and said engagement control means controls the engagement in such a manner as to maintain said engaging means in the engaged state with said receiving portion when said pedal stroke is shorter than the preset threshold value and to disengage said engaging means from said receiving portion when said pedal stroke exceeds said preset threshold value.
The present invention is characterized in that said predetermined condition is whether the power source of said booster is normal or not, and said pivotal movement control means controls the pivotal movement of said first lever member in such a manner as to prevent the pivotal movement of said first lever member when said power source is normal and to allow the pivotal movement of said first lever member when said power source fails.
In the brake pedal apparatus having the aforementioned structure, the pivotal movement control means controls the first lever member to be prevented from pivoting when the predetermined condition is not satisfied. As a result, the second lever member pivots about the second pivot pin, thereby setting the pedal leverage to correspond to the case that the predetermined condition is not satisfied. The pivotal movement control means controls the first lever member to be allowed to pivot together with the second lever member when the predetermined condition is satisfied. As a result, the second lever member pivots about the first pivot pin, thereby setting the pedal leverage to correspond to the case that the predetermined condition is satisfied. In this manner, the pedal leverage can be changed to corresponding to whether the predetermined condition is satisfied or not. Therefore, the aforementioned problems (1) through (5) can be effectively solved by variously setting the predetermined condition.
In the present invention, the input shaft of the booster or the input shaft of the master cylinder is pivotally connected to the second lever member at a position between the first pivot pin and the pedal member. Therefore, since the operating directions of the pedal member are equal to the stroke directions of the input shaft of the booster or the input shaft of the master cylinder, respectively, the booster or the master cylinder is arranged on the vehicle-front side, i.e. the side opposite to the driver, with respect to the first pivot pin. Accordingly, the brake pedal apparatus can be effectively installed in a vehicle of a type having a relatively larger space in front of a driver""s seat, for example, a vehicle of a bonnet type from the viewpoint of efficient use of space.
Moreover, in the present invention, the input shaft of the booster or the input shaft of the master cylinder is pivotally connected to the second lever member at a position opposite to the pedal member with respect to the first pivot pin. Therefore, since the operating directions of the pedal member are opposite to the stroke directions of the input shaft of the booster or the input shaft of the master cylinder, respectively, the booster or the master cylinder is arranged on the vehicle-rear side, i.e. the driver side, with respect to the first pivot pin. Accordingly, the brake pedal apparatus can be effectively installed in a vehicle of a type having a relatively small space in front of a driver""s seat, for example, a minivan from the viewpoint of efficient use of space.
In the present invention, the second lever member and the input shaft of the booster or the master cylinder are connected to each other via the third lever member, thereby increasing the degree of freedom in arrangement of the brake pedal apparatus. Accordingly, the brake pedal apparatus can be disposed below the input shaft of the booster. In this manner, the degree of freedom in arrangement of the pedal apparatus can be improved and the entire length of the assembly of the brake pedal apparatus, the booster and/or the master cylinder can be shortened.
According to the present invention, the pivotal movement control means is composed of the engaging means disposed on the first lever member, the receiving portion disposed on the vehicle body, the engagement control means for controlling the engagement between the engaging means and the receiving portion so that the pedal apparatus is structured simple.
Further in the present invention, the predetermined condition is whether the pedaling force exceeds a preset threshold value or not. When the threshold value for the pedaling force is set to be lower than that at the full load point of the booster, the brake system has the reversed two-stage servo characteristic. Therefore, since the pedal leverage is set to a smaller ratio during the normal braking when the pedaling force is smaller than the preset threshold value, that is, the predetermined condition is not satisfied, the pedal stroke can be shortened, thereby improving the pedaling feeling. Because of this reversed two-stage servo characteristic, a brake assist control (BA control) can be conducted in case of operation for emergency braking when the pedal stroke is large, thereby securing the emergency braking operation.
In case of failure of the amplifying action of the booster, since the pedaling force exceeds the preset threshold value, that is, the predetermined condition is satisfied, the pedal leverage can be changed to a larger ratio so that the driver""s operational force can be assisted to have increased braking force, thereby enabling the brake to be operated with predetermined braking force even in case of failure of the amplifying action.
Furthermore, even after the full load point of the booster, the braking force can be assisted. Also when the threshold value for the pedaling force is set to be larger than that at the full load point, the braking force can be assisted even after the full load point in the same manner.
According to the present invention, the pedal stroke is also considered as the predetermined condition in addition to the pedaling force. That is, the predetermined condition is satisfied when the pedaling force exceeds the first preset value and the pedal stroke is shorter than the second preset value. This arrangement enables more precise and effective change in pedal leverage.
According to the present invention, the pedaling speed is considered as the predetermined condition. That is, the pedal leverage is set to the larger ratio when the pedaling speed is as low as the pedaling speed for the normal braking. By setting the larger ratio to be the same as the pedal leverage for the normal braking, predetermined braking force required for the normal braking can be obtained during the operation of the service braking.
On the other hand, the pedal leverage is set to the smaller ratio by engaging the engaging means with the receiving portion when the pedaling speed is higher than the pedaling speed for the normal braking. Therefore, large braking force can be obtained with a small pedal stroke. In particular, adopting the brake pedal apparatus to a brake assist control (BA control) enables a driver such as an inexpert driver, who can depress only the same level as the normal braking, to conduct emergency braking operation without fail.
Further, in the present invention, the movement of the pedal from its inoperative position is considered as the predetermined condition. That is, when the pedal is moved backward from its inoperative position, the engaging means comes off the receiving portion by the engagement control means, thereby preventing the backward movement of the pedal from its inoperative position and preventing the pedal from colliding with the driver.
Furthermore, in the present invention, the pedal stroke is considered as the predetermined condition. That is, the pedal leverage is set to be the smaller ratio because the engaging means is maintained in the engaged state with the receiving portion by the engagement control means when the pedal stroke is small. On the other hand, the pedal leverage is set to be the larger ratio because the engaging means is disengaged from the receiving portion when the pedal stroke is large. Therefore, long stroke of the input shaft can be obtained with small pedal stroke in the initial stage of depressing the pedal when the pedal leverage is set to the smaller ratio, and large output of the input shaft can be obtained with small pedaling force when the pedal stroke is set to the larger ratio.
Therefore, employment of the brakepedal apparatus enables the pedal leverage to be set to the smaller ratio when larger input of the input shaft is not necessary but somewhat longer stroke of the input is necessary for canceling the stroke loss at the WCYs, and enables the pedal leverage to be set to the larger ratio when somewhat larger input of the input shaft is necessary but longer stroke of the input shaft is not necessary after the stroke loss is cancelled. In this manner, even with large stroke loss at the WCYs, the same pedal stroke as the conventional one can be obtained, thereby enabling the employment of the xe2x80x9czero drag caliperxe2x80x9d. This arrangement can prevent the aforementioned xe2x80x9cbrake dragxe2x80x9d, thereby reducing power loss of an engine due to the xe2x80x9cbrake dragxe2x80x9d and thus improving the fuel consumption.
Moreover, in the present invention, the failure of the power source of the booster is considered as the predetermined condition. That is, when the power source is normal, the first lever member is prevented from pivoting by the pivotal movement control means, whereby the pedal leverage is set to the small ratio for operating the service braking. Therefore, the normal braking operation can be conducted by normally depressing the pedal. In the event of failure of the power source, the first lever member is allowed to pivot by the pivotal movement control means, whereby the pedal leverage is set to be larger than the ratio for the normal braking. Because of the larger ratio, large braking force can be obtained. Therefore, even when the amplifying action of the vacuum booster fails due to the failure of the power source, predetermined braking force can be obtained, thereby ensuring the braking operation.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.